There are many thermal switching means to transfer heat between structures, such as in cryogenic refrigeration systems, also known as cryocoolers. These means are passive and operate by isolating the cryocooler and associated hardware from outside heat leaks. These devices depend on principles of thermal expansion of materials to create or tear down a thermally conductive path between structures. Thus, when a desired temperature is reached, a conductive material either expands or contracts thereby connecting or isolating a structure to be cooled or heated.
A significant limitation of these thermal switches is that they can not initiate thermal transfer on command or be tuned to control the rate of thermal transfer. For a system in which the desired thermal transfer between structures in the system is not known when the system is designed or manufactured, these types of thermal switching means will not work. Also, because these thermal switches can not be commanded to initiate or suspend thermal transfer, or be dynamically tuned to alter the rate of thermal transfer, these switches will not work in an environment or system where the thermal transfer or flow requirements between elements may change over time.